1. Field of the Invention
The present invention relates to a process for perforating plastic tubes, in particular thin-walled corrugated tubes, by means of a punching or cutting operation.
2. Description of the Prior Art
A process for perforating thinwalled polyvinylchloride tubes, whereby the produced tubes are used for drainage or irrigation in the agricultural sector, is known per se. In this known process, perforating thin-walled tubes by means of cutting or punching is effected without the presence of any supporting means inside the plastic tubes.
The known process lends itself very well to operating on thin-walled polyvinylchloride tubes with a high modulus of elasticity. Great disadvantages present themselves, however, when a thin-walled plastic tube having a low modulus of elasticity, like a polyolefinic tube, has to be perforated, as the elasticial properties of such a tube prevents a proper perforation by means of punching or cutting. The latter properties of polyolefinic material cause the material to give with the punching members; thus, no perforation of the plastic material will be effected. This disadvantage particularly occurs when the desired perforations have to be made very quickly in the recesses of corrugated tubes by means of a punching or cutting operation. Though in that case the punching members do operate upon the plastic tubes, their operation is in vain, since they do not perforate the material so that no perforations are obtained at all.
3. Summary of the Invention
The present invention aims to provide a process in which the above-mentioned disadvantages are obviated and nearly alleviated. This process is performed so that thin-walled plastics tubes having a low modulus of elasticity can be perforated rapidly by subjecting the plastic tubes to a punching or cutting operation.
This result is achieved by subjecting plastic tubes with a low modulus of elasticity, prior to punching them, to a direct or indirect treatment of a cooling fluid.
Because of this treatment, plastic tubes with a low modulus of elasticity, e.g., even when the tubes have a minor wall thickness, can be given a greater rigidity. Thus the tube material will not give with the punching or cutting members, so that the desired perforations in thin-walled plastic tubes can be punched or cut very rapidly, whether or not supporting means are present inside the tubes at the point where the punching operation takes place, that is, the punching or cutting members will no longer only move with the tube material without perforating the same.
The plastic tubes are conveniently made of a polyolefinic material, that is, preferably a polyethylene or a polypropylene material.
A very effective cooling effect of the plastic tubes is realized by spraying the tubes with a cooling liquid, preferably cooled water with a temperature ranging from about 0.degree. to 5.degree. C.
Any desired increase in the rigidity of the plastic tubes to be perforated can also be realized by cooling them with cooled air. An advantage of this medium over water is that air can be cooled to temperatures lower than 0.degree. C.
The process according to my invention has the greatest possible effectiveness when the tubes to be perforated are cooled firstly by spraying them with water having a temperature ranging from 0.degree. to 5.degree. C., while subsequently cooled air is blown upon the plastic tubes. A consequence of this treatment is that the moisture upon the outside of the tubes will be removed for the greater part, and vaporization of water will cause an accelerated cooling result. It goes without saying that in this case, dry air should be used for the blowing operation.
As described in the foregoing paragraph, thin-walled plastic tubes can be rapidly perforated by punching or cutting, and in particular punching, without any supporting means being present inside the tubes.
Perforated plastic tubes with a low modulus of elasticity, obtained by performing the process according to my invention, can be conveniently used for drainage purposes, especially in regions where low temperatures predominate. As a rule, known thin-walled polyvinylchloride tubes become brittle at low temperatures so that they are apt to break or split, even with minor vibrations.
The present invention relates also to an apparatus for perforating plastic tubes, in particular thin-walled, corrugated tubes, and comprises conveying members for conveying a plastic tube and guide means for guiding the same, as well as punching or cutting members. The apparatus is further provided with cooling members for cooling the plastic tubes to be perforated.
The apparatus conveniently includes a supporting member for supporting the plastic tubes at their outside surfaces at the point where the punching or cutting members will operate.
The cooling members are constructed effectively as a first cooling aggregate for cooling a liquid and a liquid circuit connected with nozzles which are operative in the conveying region of the plastic tubes.